The Mark Coventry Award: Patellofemoral Arthroplasty Results in Better Range of Movement and Early Patient-reported Outcomes Than TKA

Abstract

Background: Controversy exists over the surgical treatment for severe patellofemoral osteoarthritis. We therefore wished to compare the outcome of patellofemoral arthroplasty (PFA) with TKA in a blinded randomized controlled trial.

Questions/purposes: In the first 2 years after surgery: (1) Does the overall gain in quality of life differ between the implants based on the area under the curve of patient-reported outcomes (PROs) versus time? (2) Do patients obtain a better quality of life at specific points in time after PFA than after TKA? (3) Do patients get a better range of movement after PFA than after TKA? (4) Does PFA result in more complications than TKA?

Methods: Patients were eligible if they had debilitating symptoms and isolated patellofemoral disease. One hundred patients were included from 2007 to 2014 and were randomized to PFA or TKA (blinded for the first year; blinded to patient, therapists, primary care physicians, etc; quasiblinded to assessor). Patients were seen for four clinical followups and completed six sets of questionnaires during the first 2 postoperative years. SF-36 bodily pain was the primary outcome. Other outcomes were range of movement, PROs (SF-36, Oxford Knee Score [OKS], Knee injury and Osteoarthritis Outcome Score [KOOS]) as well as complications and revisions. Four percent (two of 50) of patients died within the first 2 years in the PFA group (none in the TKA group), and 2% (one of 50) became ill and declined further participation after 1 year in the PFA group (none in the TKA group). The mean age at inclusion was 64 years (SD 8.9), and 77% (77 of 100) were women.

Results: The area under the curve (AUC) up to 2 years for SF-36 bodily pain of patients undergoing PFA and those undergoing TKA was 9.2 (SD 4.3) and 6.5 (SD 4.5) months, respectively (p = 0.008). The SF-36 physical functioning, KOOS symptoms, and OKS also showed a better AUC up to 2 years for PFA compared with TKA (6.6 [SD 4.8] versus 4.2 [SD 4.3] months, p = 0.028; 5.6 [SD 4.1] versus 2.8 [SD 4.5] months, p = 0.006; 7.5 [SD 2.7] versus 5.0 [SD 3.6] months, p = 0.001; respectively). The SF-36 bodily pain improvement at 6 months for patients undergoing PFA and those undergoing TKA was 38 (SD 24) and 27 (SD 23), respectively (p = 0.041), and at 2 years, the improvement was 39 (SD 24) and 33 (SD 22), respectively (p = 0.199). The KOOS symptoms improvement at 6 months for patients undergoing PFA and those undergoing TKA was 24 (SD 20) and 7 (SD 21), respectively (p < 0.001), and at 2 years, the improvement was 27 (SD 19) and 17 (SD 21), respectively (p = 0.023). Improvements from baseline for KOOS pain, SF-36 physical functioning, and OKS also differed in favor of PFA at 6 months, whereas only KOOS symptoms showed a difference between the groups at 2 years. No PRO dimension showed a difference in favor of TKA. At 4 months, 1 year, and 2 years, the ROM change from baseline for patients undergoing PFA and those undergoing TKA was (-7° [SD 13°] versus -18° [SD 14°], p < 0.001; -4° [SD 15°] versus -11° [SD 12°], p = 0.011; and -3° [SD 12°] versus -10° [SD 12°], p = 0.010). There was no difference in the number of complications. During the first 2 postoperative years, there were two revisions in patients undergoing PFA (one to a new PFA and one to a TKA).

Conclusions: Patients undergoing PFA obtain a better overall knee-specific quality of life than patients undergoing TKA throughout the first 2 years after operation for isolated patellofemoral osteoarthritis. At 2 years, only KOOS function differs between patients undergoing PFA and those undergoing TKA, whereas other PRO dimensions do not show a difference between groups. The observations can be explained by patients undergoing PFA recovering faster than patients undergoing TKA and the functional outcome being better for patients undergoing PFA up to 9 months. Patients undergoing PFA regain their preoperative ROM, whereas patients undergoing TKA at 2 years have lost 10° of ROM. We found no differences in complications.

Level of evidence: Level I, therapeutic study.

Fig. 1 A-C

The figure shows posteroanterior (A), lateral (B), and tangential (C) radiographic projections of an eligible patient. We do not consider marginal tibiofemoral osteophytes to be a contraindication for PFA as long as the joint line width is normal.

Fig. 2

The study CONSORT diagram. Numbers in parentheses before the operation and randomization show the total number of knees at each step in the trial. One hundred knees in 100 patients were randomized per protocol. After operation/randomization, the red boxes show withdrawn patients, and the numbers in parentheses denote the number of replies and clinical assessments. At the 2-year followup in the PFA arm for instance, three of 50 patients were withdrawn (one after 9 months and two after 1 year); there are 46 clinical assessments, so one patient did not attend followup. OA = osteoarthritis.

Fig. 3

This figure presents the AUC (areas under the curve) using the OKS for a random patient in the study. The filled circles show the changes in the OKS from a value of 14 at baseline, preoperative assessment, to 44 at 2 years. The left y-axis shows the nominal values of the OKS, and the right y-axis is normalized to a scale from 0 to 1. The dark green AUC represents the overall OKS gain that this patient achieved from the operation, and using the normalized scale, the area is 10.7 months. The AUC may be interpreted in two ways. The AUC is the same size as the area of rectangle A, where the x-dimension is the number of months with normal OKS. The AUC is also the same size as the area of rectangle B, where the y-dimension is the average OKS improvement over the observation period.

Fig. 4

Area under the OKS improvement curve up to 2 years for individual patients versus baseline OKS. There is a significant negative slope (r = -0.637, p < 0.001 and r = -0.421, p = 0.007 for patients undergoing PFA and those undergoing TKA, respectively) demonstrating that patients with a lower preoperative score obtain a larger improvement. The regression lines for patients undergoing PFA and those undergoing TKA do not intersect, and PFA gives a uniformly better result than TKA.

Fig. 5

Paired differences (relative to baseline) for the eight dimensions of the SF-36 system are demonstrated. Probability values are results of comparisons of PFA and TKA at individual time points. Significant differences are in bold. Error bars signify ± 1 standard error of mean.

Fig. 6

Paired differences (relative to baseline) for the eight dimensions of the KOOS system are shown. Probability values are results of comparisons of PFA and TKA at individual time points. Significant differences are in bold. Error bars signify ± 1 standard error of mean.

Fig. 7

Paired differences of the OKS showing the improvement at different time points after the operation. The errors bars signify ± 1 standard error of the mean. The p values resulting from a comparison of the two groups are shown at the top of the graph.

Fig. 8

Variations in paired differences for ROM over time. The horizontal solid line signifies the baseline ROM. The p values below the curves are the results of t-tests of the PFA group versus the TKA group. The p values above the horizontal solid line are the results of tests of difference from the baseline ROM for the PFA and TKA groups. Two weeks after the operation, the ROM decreased approximately 50° for both groups. At later time points, the decrease in ROM was significantly larger for the TKA group. The PFA group had regained the baseline ROM by 1 year, whereas the TKA group had not regained the baseline ROM by 2 years. Error bars indicate ± 1 standard error of mean.